From scratch


TDPRI Member
Sep 4, 2016
Claremore, OK

I've been building and moding amps for a few years now, but this was the first time where I really made a circuit my own, and created my own layout. I started with a basic AB7563 Blackface circuit as cut down to a single channel by Rob Robbinette. I started with his RR763 dual 6L6 design. From there, I added or changed the following:

1. Upped transformers to support four 6L6GC tubes for 85 watts.

2. Switchable true bypass effects loop added between the volume control and pin 7 of V1.

3. Presence control

4. Removed the RR763 Mix and Load resistors and replaced them with a 250K pot wired as a variable resistor. This acts as the gain control.

5. Vox Tone Cut for clipping ice pick highs.

6. Switchable Master Volume

7. Variable Negative Feedback control for a wider variety of tones.

8. 3 position "Gain Switch" which varies the V1 negative feedback and bypass cap.

9. Preamp plate load resistors changed to 220k

10. Power tube grid leaks changed to 100k

11. Mute switch

All in all the amp sounds quite good! I'm going to play with the coupling cap values to decrease some of the low end. But! All in all I'm really happy. With the gain turned down, and the MV out of the circuit, it's classic blackface. But with the gain in, it's very early Boogie. I'm quite proud of how it turned out.

I want to thank @robrob for the incredible resource that is both his site and the man himself.